The present invention relates to resilient electrical contact (interconnection) elements (structures), also referred to as spring contacts, suitable for effecting pressure connections between electronic components and, more particularly, to microminiature spring contacts such as may be used in probing (resiliently and temporarily contacting) microelectronic components such as active semiconductor devices.
Commonly-owned U.S. patent application Ser. No. 08/152,812 filed Nov. 16, 1993 (now U.S. Pat. No. 4,576,211, issued Dec. 19, 1995), and its counterpart commonly-owned copending xe2x80x9cdivisionalxe2x80x9d U.S. patent applications Ser. No. 08/457,479 filed Jun. 01, 1995 (status: pending) and Ser. No. 08/570,230 filed Dec. 11, 1995 (status: pending), all by KNANDROS, disclose methods for making resilient interconnection elements for microelectronics applications involving mounting an end of a flexible elongate core element (e.g., wire xe2x80x9cstemxe2x80x9d or xe2x80x9cskeletonxe2x80x9d) to a terminal on an electronic component coating the flexible core element and adjacent surface of the terminal with a xe2x80x9cshellxe2x80x9d of one or more materials having a predetermined combination of thickness, yield strength and elastic modulus to ensure predetermined force-to-deflection characteristics of the resulting spring contacts. Exemplary materials for the core element include gold. Exemplary materials or the coating include nickel and its alloys. The resulting spring contact element is suitably used to effect pressure, or demountable, connections between two or more electronic components, including semiconductor devices.
Commonly-owned, copending U.S. patent application Ser. No. 08/340,144 filed Nov. 15, 1994 and its corresponding PCT Patent Application No. PCT/US94/13373 filed Nov. 16, 1994 (WO95/14314, published May 26, 1995), both by KHANDROS and MATHIEU, disclose a number of applications for the aforementioned spring contact element, and also disclosed techniques for fabricating contact pads at the ends of the spring contact elements. For example, in FIG. 14 thereof, a plurality of negative projections or holes, which may be in the form of inverted pyramids ending in apexes, are formed in the surface of a sacrificial layer (substrate). These holes are then filled with a contact structure comprising layers of material such as gold or rhodium and nickel. A flexible elongate element is mounted to the resulting contact structure and can be overcoated in the manner described hereinabove. In a final step, the sacrificial substrate is removed. The resulting spring contact has a contact pad having control led geometry (e.g., sharp points) at its free end.
Commonly-owned, copending U.S. patent application Ser. No. 08/452,255 filed May 26, 1995 and its corresponding PCT Patent Application No. PCT/US95/14909 filed Nov. 13, 1995 (WO96/17278, published Jun. 06, 1996), both by ELDRIDGE, GRUBE, KHANDROS and MATHIEU, disclose additional techniques and metallurgies for fabricating contact tip structures on sacrificial substrates, as well as techniques for transferring a plurality of spring contact elements mounted thereto, en masse, to terminals of an electronic component (see, e.g., FIGS. 11A-11F and 12A-12C therein).
Commonly-owned, copending U.S. Provisional Patent Application No. 60/005,189 filed May 17, 1996 and its corresponding PCT Patent Application No. PCT/US96/08107 filed May 24, 1996 (WO96/37332, published Nov. 28, 1996), both by ELDRIDGE, KHANDROS, and MATHIEU, discloses techniques whereby a plurality of contact tip structures (see, e.g, #620 in FIG. 6B therein) are joined to a corresponding plurality of elongate contact elements (see, e.g., #632 of FIG. 6D therein) which are already mounted to an electronic component (#630). This patent application also discloses, for example in FIGS. 7A-7E therein, techniques for fabricating xe2x80x9celongatexe2x80x9d contact tip structures in the form of cantilevers. The cantilever tip structures can be tapered, between one end thereof and an opposite end thereof. The cantilever tip structures of this patent application are suitable for mounting to already-existing (i.e., previously fabricated) raised interconnection elements (see, e.g., #730 in FIG. 7F) extending (e.g., free-standing) from corresponding terminals of an electronic component (see. e.g., #734 in FIG. 7F).
Commonly-owned, copending U.S. Provisional Patent Application No. 60/024,555 filed Aug. 26, 1996, by ELDRIDGE, KHANDROS and MATHIEU, discloses, for example at FIGS. 2A-2C thereof, a technique whereby a plurality of elongate tip structures having different lengths than one another can be arranged so that their outer ends are disposed at a greater pitch than their inner ends. Their inner, xe2x80x9ccontactxe2x80x9d ends may be collinear with one another, for effecting connections to electronic components having terminals disposed along a line, such as a centerline of the component.
The present invention addresses and is particularly well-suited to making interconnections to modern microelectronic devices having their terminals (bond pads) disposed at a fine-pitch. As used herein, the term xe2x80x9cfine-pitchxe2x80x9d refers to microelectronic devices that have their terminals disposed at a spacing of less than 5 mils, such as 2.5 mils or 65 xcexcm. As will be evident from the description that follows, this is preferably achieved by taking advantage of the close tolerances that readily can be realized by using lithographic rather than mechanical techniques to fabricate the contact elements.
An object of the present Invention is to provide an improved technique for fabricating spring contact elements.
Another object of the invention is to provide a technique for fabricating spring contact elements using processes that are inherently well-suited to the fine-pitch close-tolerance world of microelectronics.
Another object of the invention is to provide a technique for fabricating spring contact elements that are suitable for probing electronic components such as semiconductor devices, and that is readily scaleable to probing fine-pitch peripheral interconnect structures.
Another object of the invention is to provide a technique for fabricating spring contact elements that are suitable for socketing electronic components such as semiconductor devices, such as for performing burn-in on said devices.
According to the invention, an elongate spring contact element suitable for microelectronic applications is fabricated by forming depressions (such as trenches, such as by etching) in a sacrificial substrate and depositing (such as by plating) metallic materials into the depressions. A plurality of spring contact elements may be fabricated in this manner on a single sacrificial substrate, with lithographically-defined tolerances (e.g., dimensions, spacings).
The resulting spring contact elements may then be mounted to another substrate such as a passive substrate or an active substrate such as a semiconductor device, after which the sacrificial substrate is removed.
An exemplary spring contact element formed in this manner has a length xe2x80x9cLxe2x80x9d between its base end and its contact end. The base end is preferably offset in a first direction from a central portion of the spring contact element, and the contact end is preferably offset in an opposite direction from the central portion. In this manner, the overall spring contact element is not planar and, when its base end is mounted to an electronic component, its contact end extends above the surface of the electronic component to which it is mounted.
An exemplary sacrificial substrate upon which the spring contact elements may be fabricated is a silicon wafer, in which case the process of the present invention advantageously utilizes the directionally selective etching of silicon used for micro-machining processes to create an electroform which is used to plate up the final spring contact element. This approach may optionally employ laser-based ablation of photoresist, as opposed to lithographic development of the photoresist, in order to create the high aspect ratio of width to height which is required for fine pitch spacings between the spring contact elements.
An exemplary application for the spring contact elements of the present invention is as probe elements used to effect pressure connections between a substrate and a device-under-test (DUT), in which case the spring contact elements are suitably mounted to a space transformer component of a probe card assembly, such as is described in the aforementioned Ser. No. 08/554,902 and PCT/US95/14844. Alternatively, the spring contact elements are mounted to and extend from an active electronic component such as an application specific integrated circuit (ASIC).
The spring contact element is suitably formed of at least one layer of a metallic material selected for its ability to cause the resulting contact structure to function, in use, as a spring (i.e., exhibit elastic deformation) when force is applied to its contact (free) end.
The resulting spring contact element is preferably xe2x80x9clong and lowxe2x80x9d, having:
a length xe2x80x9cLxe2x80x9d, as measured from one end to another end;
a height xe2x80x9cHxe2x80x9d measured transverse the length in a direction that is normal (z-axis) to the surface of the sacrificial substrate (and, normal to the component to which the spring contact element is ultimately mounted);
a contact end portion which is offset in a one direction (e.g., negative along the z-axis) from a central portion of the spring element by a distance xe2x80x9cd1xe2x80x9d; and
a base end portion which is offset in one direction (e.g., positive z-axis) from the central portion of the spring element by a distance xe2x80x9cd2xe2x80x9d.
The spring contact element is preferably tapered from the one (base) end to the other (contact) end thereof, the spring contact element having the following dimensions:
a width xe2x80x9cw1xe2x80x9d at its base end as measured parallel to the surface of the sacrificial substrate and transverse to the longitudinal axis of the spring element;
a width xe2x80x9cw2xe2x80x9d at its contact end as measured parallel to the surface of the sacrificial substrate and transverse to the longitudinal axis of the spring element;
a thickness xe2x80x9ct1xe2x80x9d at its base end, measured along the z-axis; and
a thickness xe2x80x9ct2xe2x80x9d at its contact end, measured along the z-axis;
resulting in:
a widthwise taper angle xe2x80x9cxcex1xe2x80x9d (alpha); and
a thickness taper angle xe2x80x9cxcex2xe2x80x9d (beta).
The spring contact element is also suitably provided with a projecting feature at its contact end, said feature having a dimension xe2x80x9cd3xe2x80x9d measured along the z-axis.
There is thus described herein an exemplary spring contact element suitable for effecting connections between two electronic components, tropically being mounted by its base end to a one of the two electronic components and effecting a pressure connection with its contact end (e.g., by the projecting feature) to an other of the two electronic components, having the following dimensions (in mils, unless otherwise specified):
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.